Geant4 Simulation Research Articles

GPU-accelerated calculation of proton microdosimetric spectra as a function of target size, proton energy, and bounding volume size

Objective. Shortcomings of dose-averaged linear energy transfer (LETD), the quantity which is most commonly used to quantify proton relative biological effectiveness, have long been recognized. Microdosimetric spectra may overcome the limitations of LETD but are extremely computationally demanding to calculate. A systematic library of lineal energy spectra for monoenergetic protons could enable rapid determination of microdosimetric spectra in a clinical environment. The objective of this work was to calculate and validate such a library of lineal energy spectra. Approach. SuperTrack, a GPU-accelerated CUDA/C++ based application, was developed to superimpose tracks calculated using Geant4 onto targets of interest and to compute microdosimetric spectra. Lineal energy spectra of protons with energies from 0.1 to 100 MeV were determined in spherical targets of diameters from 1 nm to 10 μm and in bounding voxels with side lengths of 5 μm and 3 mm. Main results. Compared to an analogous Geant4-based application, SuperTrack is up to 3500 times more computationally efficient if each track is resampled 1000 times. Dose spectra of lineal energy and dose-mean lineal energy calculated with SuperTrack were consistent with values published in the literature and with comparison to a Geant4 simulation. Using SuperTrack, we developed the largest known library of proton microdosimetric spectra as a function of primary proton energy, target size, and bounding volume size. Significance. SuperTrack greatly increases the computational efficiency of the calculation of microdosimetric spectra. The elevated lineal energy observed in a 3 mm side length bounding volume suggests that lineal energy spectra determined experimentally or computed in small bounding volumes may not be representative of the lineal energy spectra in voxels of a dose calculation grid. The library of lineal energy spectra calculated in this work could be integrated with a treatment planning system for rapid determination of lineal energy spectra in patient geometries.

OPSimTool: A custom tool for optical photon simulation in Geant4

This paper introduces OPSimTool, a set of additions to the Geant4 toolkit that simplify the development of optical photon applications and enhance the flexibility and maintainability of developed applications. The tool also provides interfaces for creating reusable and portable material build code. This tool has been developed according to users' needs and perspectives, considering frequently asked questions, most encountered challenges, and evolving needs over time in the optical category of the Geant4 official forum page. Program summaryProgram title: OPSimToolCPC Library link to program files:https://doi.org/10.17632/6jtbxdnpm4.1Developer's repository link:https://github.com/mkandemirr/OpSimLicensing provisions: GNU General Public License 3Programming language: C++External routines/libraries: Geant4, CMakeNature of problem: Although the toolkit provided by Geant4 is sufficient to perform optical photon simulations, providing additional tools will be highly beneficial for developing more flexible and sustainable applications.Solution method: We have developed a set of C++ classes in the spirit of Geant4 users and made them available to the public.

Dosimetric Investigation of Six Ru-106 Eye Plaques by EBT3 Radiochromic Films and Monte Carlo Simulation.

Ophthalmic brachytherapy using radioactive plaques is an effective technique for the treatment of uveal melanoma. Ru-106 eye plaques are considered as interesting issue due to their steep gradient dose. The pre-planning evaluation of dosimetric parameters is essential for the treatment planning system. The current study aims at providing dose distributions of six Ru-106 eye plaques (CCA, CCB, CGD, CIB, COB and COD) using radiochromic EBT3 film, Geant4 Monte Carlo toolkit and the treatment planning software (Plaque Simulator). In this experimental study, an in-house phantom was employed for depth dose measurements with EBT3 films. Also, Geant4.10.5 scoring mesh was implemented to obtain the 2D dose distribution of the plaques. The results were compared with Plaque Simulator software and the manufacturer's (BEBIG) data. The gamma index criterion (3%/3 mm) was used to evaluate dose distributions obtained by the film measurements and Geant4 simulation. A good agreement was achieved between simulation and experimental results. Gamma index passing rate was 94.2%, 89.3%, 88.2%, 82.2%, 92.2% and 90.1% for CCA, CCB, CGD, CIB, COB and COD plaques, respectively. Absolute dose rate (mGy/min) obtained by EBT3 film at the depth of 2 mm was 79.4 mGy/min, 81.0 mGy/min, 78.6 mGy/min, 62.2 mGy/min, 75.2 mGy/min and 81.2 mGy/min for CCA, CCB, CGD, CIB, COB and COD plaques, respectively. The measured dose distributions and lateral dose profiles may be utilized in the treatment planning system to cover clinical volumes such as the clinical target volume and the gross tumor volume.

DREAM: A Miniaturized Spectrometer for Measurement of Protons and Electrons on Orbit

CNES (Centre National d’Etudes Spatiales) is currently developing a new instrument called DREAM (Détecteur Radiation Energétique Adaptable et Miniaturisé) in order to measure electrons and protons in the Earth magnetosphere. Compared to the instrument ICARE-NG (Influence sur les Composants Avancés des Radiations de l’Espace - Nouvelle Génération), DREAM is compatible with nanosatellite cubesats. In this article, we present the instrument architecture, new sensors design, hardware improvements and first results. Response functions for protons and electrons sensors are calculated using GEANT4 (Geometry And Tracking) simulations. The calculation of predicted count rates of particles is performed.

Mechanic-elastic properties and radiation attenuation efficiency of TeO2/WO3/K2O composite glass systems for nuclear and medical application

WO3 effects on neutron and ionizing radiation defending factors of ternary tellurite-based glass blocks with molecular formula 80TeO2 –(20-x)WO3 – xK2O; x = 0–20 mol% (denoted as TKW-glass) has been reported via Phy-X theoretical calculations and Geant4 simulation code. Correlations between shielding factors and kinetics properties of the investigated glasses at different photon energy have been examined. The highest values of mass (MAC) attenuation coefficient were noted at 15 keV of the examined TKW-glass materials with the values of 38.408, 44.388, 49.855, 54.872, 59.492 cm2/g for TKW-0, TKW-5, TKW-10, TKW-15, and TKW-20, respectively. Generally, these values of the TKW-glasses obey the sequence: (TKW-0)MAC< (TKW-5)MAC < (TKW-10)MAC < (TKW-15)MAC < (TKW-20)MAC. The highest mean free path (MFP) values of TKW-glasses were registered at 15 MeV with the values of 6.101, 5.591, 5.097, 4.647, and 4.302 cm for TKW-0, TKW-5, TKW-10, TKW-15, and TKW-20, respectively. The two parameters half value layer (HVL) and MFP follow the pattern: (TKW-0)HVL, MFP > (TKW-5)HVL,MFP > (TKW-10)HVL,MFP > (TKW-15)HVL,MFP > (TKW-20)HVL,MFP. The maximum values of effective atomic number (EAN) took place at gamma energy of 15 keV corresponding to 44.35, 48.86, 52.63, 55.83, and 58.58 for TKW-0, TKW-5, TKW-10, TKW-15, and TKW-20, respectively. The trend of the buildup factors was similar for all of the glass specimens. The fast neutron removal cross-section (ΣR) enhanced as WO3 content increased in the specimens. Thus, the peaked value of ΣR is 0.1059 cm−1 was noted in the TKW-20 sample. Mechanical properties, neutron and γ-rays protection parameters were observed to improve with enhanced WO3 mol% in the TKW-glasses. The current results bear their utilization for neutron and gamma protection purposes.

True coincidence summing correction for a BEGe detector in close geometry measurements

The true coincidence summing correction factor for a Broad Energy Germanium detector has been calculated at far and close geometry set-up using radioactive γ-ray sources. The correction factors were calculated using both experimental and analytical methods. Geant4 simulation was done to calculate the full-energy peak and total efficiencies of the detector. Standard, as well as fabricated mono-energetic γ-ray sources, were used for the γ-ray efficiency measurements. The simulated efficiencies of mono-energetic γ-ray sources were matched to the experimental γ-ray efficiencies by optimizing the detector parameters. The same parameters were used to obtain the full-energy peak and total efficiencies for γ-rays of current interest. Analytical and experimental correction factors were found to agree well with each other. The coincidence summing effect is found to be significant for source-to-detector distances less than 5 cm.

Geant4 simulation of energy deposition ratio and physical processes of CdZnTe crystals irradiated by high energy particles

Geant4 simulation of energy deposition ratio and physical processes of CdZnTe crystals irradiated by high energy particles

Calculation and verification of multi-MeV photon scattering coefficient

It is necessary to estimate the scattering radiation contribution accurately and quickly in the radiation shielding calculation and design, and the photon scattering coefficient is a key parameter in this process. In real engineering applications, the radiation source is typically a multi-MeV photon beam, however, it can be challenging to determine precise parameters from the available literature. In this work, we used the Geant4 Monte Carlo code to simulate the scattering coefficients of monoenergetic photons with incident energies between 0.01 and 20 MeV at all angles of reflection with different scattering materials and thickness, and built a database, the Geant4 simulated results are in good agreement with the literature data. It then presents an algebraic approach and develops a MATLAB program to calculate multi-MeV photon scattering coefficient based on monoenergetic photon scattering coefficient simply by importing the photon spectrum. The results calculated using this approach basically coincide with Geant4 simulation, and agree well with the experimental results within the error range allowed. We can more accurately estimate the scattering radiation dose at the point of interest with the aid of a theoretical formula through this approach, thus significantly improve the computational efficiency in engineering radiation shielding calculation and design.

Characterizing Low-Energy Charged Particles in the Magnetosphere with the LEM CubeSat Spectrometer Project: Detector Concept and Hardware Characterisation

An accurate flux measurement of low-energy charged particles trapped in the magnetosphere is necessary for space weather characterization and to study the coupling between the lithosphere and magnetosphere, which allows for the investigation of the correlations between seismic events and particle precipitation from Van Allen belts. In this work, the project of a CubeSat space spectrometer, the low-energy module (LEM), is shown. The detector will be able to perform an event-based measurement of the energy, arrival direction, and composition of low-energy charged particles down to 0.1 MeV. Moreover, thanks to a CdZnTe mini-calorimeter, the LEM spectrometer also allows for photon detection in the sub-MeV range, joining the quest for the investigation of the nature of gamma-ray bursts (GRBs) and terrestrial gamma-ray flashes (TGFs). The particle identification of the LEM relies on the ΔE−E technique performed by thin silicon detectors. This multipurpose spectrometer will fit within a 10 × 10 × 10 cm3 CubeSat frame, and it will be constructed as a joint project between the University of Trento, FBK, and INFN-TIFPA. To fulfil the size and mass requirements, an innovative approach, based on active particle collimation, was designed for the LEM; this avoids the heavy/bulky passive collimators of previous space detectors. In this paper, we will present the LEM geometry, its detection concept, the results from the developed GEANT4 simulation, and some characterisations of a candidate silicon detector for the instrument payload.

Neutron yield using a semi-Monte Carlo simulating method for D-T fusion neutron sources

Neutron yield and spatial distribution are crucial parameters of a gaseous target D-T neutron source. The exact calculation of these parameters in large-size geometries with complex fluid dynamics is very important for gaseous target neutron source design and subsequent applications. The gaseous target on operating conditions put more requirements on the Multiphysics simulating method. The fusion neutron yield simulating method has been developed using semi-Monte Carlo based on the finite element analysis for Multiphysics. The method has been verified using the model of a D-T fusion neutron source with a windowless gas target and compared with experimental results and the GEANT4 simulations. Compared with the experimental results, the simulated neutron yield error is 8.31%, and compared with the result of GEANT4, the relative error of total neutron yield is 3.34%. The spatial distributions of neutron yield are in good agreement with the results of GEANT4. In particular, the computing time is reduced from ∼200 core-hours with GEANT4 to ∼50 core-hours with the developed semi-Monte Carlo method, greatly improving the calculation efficiency.

Geant4 simulation of the moderating neutrons spectrum

In this paper we deal with the problem of predicting a steady-state neutron spectrum in media of arbitrary composition and geometry. The analytical calculations of such spectrum are often too complex, if at all possible. We describe a method of Geant4-based Monte Carlo calculation of the steady-state neutron spectrum in a medium containing a fixed neutron source. In addition to the steady-state spectrum, we obtain the snapshots of the neutron spectrum evolution in time, which may be thought of as the non-equilibrium neutron spectra, and their form is of considerable interest for further studies.

Reduction in radioactivity-induced backgrounds using a novel active veto detector for rare event search experiments

The results of a newly developed annular cryogenic phonon-mediated active veto detector are discussed which shows a significant reduction of radioactivity-induced backgrounds in rare event search experiments. The veto detector is made up of germanium weighing ∼500 g with an outer diameter of 76 mm and an inner diameter of 28 mm. The detector can host a 25 mm diameter germanium inner target detector of mass ∼10 g. A GEANT4 simulation with the active veto and inner target detector shows a gamma background reduction of 50 - 80% which is further improved (&gt; 90%) with 4pi veto coverage. Experimental measurements with the detector assembly agree well with the simulation.

The Correlation Between Scatter Detector Performance and Spatial Resolution in a Ring-Shaped Compton Imaging System

Whole gamma imaging (WGI) is a new concept that combines PET and Compton imaging by inserting a scatter detector ring into a PET ring. We developed a WGI prototype and demonstrated three-dimensional tomographic Compton imaging of a 89Zr-injected mouse. However, improving the scatter detector performance, i.e. crystal pitch and energy resolution, was required for high resolution Compton imaging. Therefore, we investigated the correlation in Geant4 simulations using 909 keV gamma rays emitted from 89Zr. Three WGI geometries consisting of the scatter detector ring with different GAGG crystal sizes (0.9 W 0.9 W 6 mm3, 1.45 W 1.45 W 6 mm3 and 2 W 2 W 6 mm3) were modeled. The energy resolutions were obtained experimentally for application to the simulation data. Also, the values were virtually halved and 1.5 times degraded. Simulations of a point-like source were carried out varying the pixel pitch in the scatter detector and images were reconstructed. For a source placed at the center of the system, a spatial resolution of 1.7, 1.9 and 2.3 mm was obtained with pixel pitches of 0.9, 1.45 and 2 mm, respectively. The spatial resolution of the system obtained with the 0.9 mm scatterer was improved to 1.4 mm for the halved energy resolution and it was deteriorated to 2.1 mm for the 1.5 times degraded energy resolution. In the hot-rod-like phantom simulation, 2 mm diameter rods were separated in the reconstructed images with the 0.9 mm scatterer. The separation became clearer for the halved energy resolution.

Geant4 simulation model of electromagnetic processes in oriented crystals for accelerator physics

Geant4 simulation model of electromagnetic processes in oriented crystals for accelerator physics

DoseMRT: A Software Package for Individualised Monte Carlo Dose Calculations of Synchrotron-Generated Microbeam Radiation Therapy

This work describes the creation and experimental validation of DoseMRT, a new software package, and its associated workflow for dose calculations in synchrotron-generated broad beam and microbeam radiation treatment fields. The DoseMRT software package allows users to import CT DICOM datasets into Geant4 for Monte Carlo dose calculations. It also provides basic treatment planning capabilities, simplifying the complexity of performing Geant4 simulations and making our Monte Carlo dose calculation algorithm accessible to a broader range of users. To demonstrate the new package, dose calculations are validated against experimental measurements performed in homogeneous water tank phantoms and the anatomically complex Alderson Radiotherapy Phantom for both broad-beam and microbeam configurations. Additionally, DoseMRT is successfully utilised as the primary method for patient-specific treatment prescription in an in vivo experiment involving tumour-bearing rats at the Imaging and Medical Beamline of the Australian Synchrotron.

Average photonuclear cross section measurements for the 141Pr, 160Gd and 162Er isotopes and compared with Geant4 simulations

Average photonuclear cross section measurements for the 141Pr, 160Gd and 162Er isotopes and compared with Geant4 simulations

Correlation between respiratory-induced target motion and dosimetric variance on EBRT

During radiation therapy, it is crucial to realise adequate dose coverage of the target at depth. However, physicists must overcome many challenges before they can achieve better accuracy. Respiratory-induced organ motion (RIOM) remains a challenge that negatively contributes to external beam radiotherapy (EBRT) accuracy. Although the magnitude of respiratory motion amplitude is a major factor in maximising or minimising the dosimetric effect of respiratory motion, other factors may negatively or positively contribute to this effect. This study investigated the impact of respiratory motion and tumour parameters, amplitude, and volume, on gross tumour volume (GTV) coverage during EBRT. In addition, it analysed the impact of tumour volume on the dosimetric effect of RIOM. A GEANT4 code was used for simulating the in vivo interaction of matter with ionising radiation was used to provide a model of respiratory-induced organ motion and voxel-level dosimetry of a simulated target. Thirty different setups were simulated using the GEANT4 simulation toolkit. Each setup demonstrated how a specific combination of respiratory and tumour parameters, amplitude, and size impact GTV coverage. The results show that the dosimetric effect of respiratory motion depends more on respiratory parameters i.e. on the respiratory motion amplitude. The reduction in GTV coverage for a tumour of 5 mm diameter can vary from approximately 28%–67%. At a certain respiratory amplitude, the tumour size can strongly affect GTV coverage. This effect becomes more dominant when the respiratory amplitude exceeds the tumour diameter. This study shows that any approach to compensate for RIOM in EBRT should consider the role of tumour size.

A review of the Geant4 simulation platform for applications involving optical-based sensing and dosimetry

Geant4 is a versatile simulation platform for numerous applications involving transport of ionizing radiation, including ionizing photons. Moreover, the physics needed for tracking optical photons is also embedded in the Geant4 simulation toolkit. From its introduction two decades ago there have been a variety of reports concerning the use of the Geant4 code in optical photons transport applications. Further to this, in particular for the interests herein, characterizations of radioluminescence radiation detectors have also been conducted. Noting the rapid development of such detectors, reliant on light collection and detection, there has been an implicit need for optimization of the different components forming the respective optical devices. Compared to ionizing radiation transport modeling less attention has been paid to this capability among the radiation physics community and Geant4 users. This review first describes in brief terms the physics built into Geant4 to provide for the transport of optical photons. This is followed by a retrospective on reported applications, discussion of the strengths and deficiencies of optical transport analyses by Geant4 and contemplation of possible future applications.

Geant4 Simulation of Muon Absorption in Concrete Layers

Muography requires a detailed understanding of the absorption of muons in the material situated between the muon source and the detector. A large-statistics (&gt;3 billion event) Geant4 simulation was run to simulate the absorption of muons in different thicknesses of concrete layers and to determine the effect of the material on the energies of muons that were not absorbed. The Geant4 simulation included a simple detector placed directly behind the absorbing material. A Geant4 simulation was also run for the same detector for alpha sources with no absorbing material and the results of this simulation were compared to the signals from the physical detector built in the laboratory and measured using standard alpha sources. The large-statistics simulations using muons of different energies were compared to the predictions of muon absorption from existing literature. The results of the simulations were in good agreement with both the measured signals from the laboratory as well as the predictions from the literature and the general method is found to be well-suited for studies used for muography involving material layers of uniform thickness.

Evaluation of neutron doses in Brazilian aircrew by the Monte Carlo method

The demand for air travel has intensified over the last few decades and, accordingly, studies seeking to assess the levels of exposure to cosmic radiation that aircrew and frequent passengers are subject to have attracted more and more interest. Aircrew, for frequently manning high altitude flights, appear as professionals directly exposed and prone to the risks arising from cosmic radiation. Continuous exposure to particles of cosmic origin can lead to dose levels above the regulatory limits for public exposure, with neutrons being the particles of the highest contribution to the dose. In several countries around the world, aircrew already have regulatory control in terms of radiological protection and are classified as occupationally exposed. In Brazil, however, there is neither a regulatory control nor a specific classification for these professionals. The objective of this work is to estimate both the neutron component of the effective dose and the effective dose of Brazilian aircrew due to cosmic rays using the GEANT4 Monte Carlo toolkit. For the estimation of the effective dose, the EXPACS code was used to estimate the neutron flux and GEANT4 to obtain the doses on the selected flights. The GEANT4 simulations were performed in the flight conditions and with ICRP voxel phantoms. The neutron doses obtained ranged from 0.002 to 3.0 mSv on the different selected flights.The equivalent doses of neutrons, in certain organs, were also estimated. In the end, the total effective doses were presented, with the contribution of neutron doses, and, when compared with the annual dose limits for members of the public and occupationally exposed workers, they showed that aircrew could receive dose levels above the public limit. A comparison was made with experimental dose measurements throughout the Brazilian territory.